Doesn't appear to be restricted to Uber One members, but likely is targeted. Not limited to $40 orders as with the last offer. Otherwise a good way to get some cheap groceries if you can hit as close to $20 as possible!
Edit: Just got burnt by ordering olive oil and three bananas, but they had no olive oil so my three bananas ending up costing $5 :(
In retrospect I should have just stuck to essentials or only multiples of a single item so at least if the product isn't available the order is cancelled instead.
Took advantage of this last night. Three orders just over $20 + $0.99 delivery.